1. Field of the Invention
One embodiment of the present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
Note that in this specification, a semiconductor device generally means a device which can function by utilizing semiconductor characteristics. An electrooptic device, a light-emitting display device, a semiconductor circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
A technique in which a transistor is formed using a semiconductor thin film has attracted attention. The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device (also simply referred to as a display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor. As another material, an oxide semiconductor has attracted attention.
For example, a technique is disclosed by which a transistor is formed using zinc oxide or an In—Ga—Zn-based oxide as an oxide semiconductor (see Patent Documents 1 and 2).
In addition, a technique in which oxide semiconductor layers with different electron affinities (or conduction band minimum states) are stacked to increase the carrier mobility of a transistor is disclosed (see Patent Documents 3 and 4).
In recent years, demand for an integrated circuit in which transistors and the like are integrated with high density has risen with reductions in the size and weight of an electronic device.